Roller drive

ABSTRACT

A high speed ratio drive system is formed of planet rollers, each having varying diameter, an outer fixed ring in contact with one diameter of the planet rollers, and an outer drive ring in contact with another diameter of the planet rollers. An inner drive element is provided by a sun drive roller in contact with the planet rollers or by a planet carrier. Preferably the system has an axial reflective symmetry minimizing twisting forces on the planet rollers.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit under 35 USC 119(e) of U.S.provisional application Ser. no. 61/933,522 filed Jan. 30, 2014.

TECHNICAL FIELD

Large speed ratio power transmission.

BACKGROUND

The present device is in the technical field of power transmission. Moreparticularly the present device lies in the technical field of frictiondrive power transmission. More specifically, the present invention is inthe field of large speed ratio differential friction drive powertransmission. The present invention relates to, but is not limited tothe field of robotic actuators.

SUMMARY

In an embodiment, there is disclosed a drive system comprising rollers,each roller having a first portion of a first diameter and a secondportion of a second diameter, a fixed outer ring arranged in rollingcontact with the respective first portion of each roller, and an outerdrive or driven ring arranged in rolling contact with the respectivesecond portion of each roller.

The rollers may be planet rollers and may be arranged about a sunroller. In further embodiments, there may be included one or more of thefollowing: the drive system may be arranged as a speed reducer in whichthe sun drive roller provides an input and the outer driven ringprovides an output; the drive system may be arranged as a speedincreaser in which the sun drive roller provides an output and the outerdrive ring provides an input; there may be a floating sun rollerarranged in rolling contact with the respective second portion of eachroller, the sun drive roller being arranged in rolling contact with therespective first portion of each roller; and there may be a floating sunroller arranged in rolling contact with the respective first portion ofeach roller, the sun drive roller being arranged in rolling contact withthe respective second portion of each roller.

In another embodiment, the drive system may have a planet carrier driveelement arranged to rotate with the planet rollers around an axisdefined by the outer drive or driven ring. In further embodiments, thedrive system may be arranged as a speed reducer in which the planetcarrier drive element provides an input and the outer driven ringprovides an output; the drive system may be arranged as a speedincreaser in which the planet carrier drive element provides an outputand the outer drive ring provides an input; and there may be a firstfloating sun roller arranged in rolling contact with the respectivefirst portion of each planet roller and a second floating sun rollerarranged in rolling contact with the respective second portion of eachplanet roller.

In various embodiments there may be included one or more of thefollowing: the first diameter may be greater than the second diameter,the first diameter may be less than the second diameter, there may be asecond fixed outer ring, the fixed outer ring and second fixed outerring being arranged symmetrically one on each side of the outer drive ordriven ring; there may be a second outer drive or driven ring, the outerdrive or driven ring and the second outer drive or driven ring beingarranged symmetrically one on each side of the fixed outer ring, andbeing connected to each other to rotate together; there may be gearteeth on one or more pairs of surfaces in rolling contact; the rollersmay be tapered, with respective tapered portions narrowing inwardly oroutwardly; surfaces contacting the respective tapered portions may becorrespondingly tapered, surfaces contacting the respective taperedportions may be tapered in ratios corresponding to the ratios of thediameters the respective elements at the contacting surfaces; the planetrollers may have a reflective symmetry with respect to a plane, therollers defining respective axes perpendicular to the plane; and theelements in rolling contact with the planet rollers may define axesperpendicular to the plane and collectively have a reflective symmetrywith respect to the plane.

BRIEF DESCRIPTION OF THE FIGURES

Embodiments will now be described with reference to the figures, inwhich like reference characters denote like elements, by way of example,and in which:

FIG. 1 is isometric view of a preferred embodiment of a high ratiorolling contact speed change device;

FIG. 2 is a side view of the device of FIG. 1;

FIG. 3 is a section view of the device of FIG. 1;

FIG. 4 is an isometric section view of a floating sun roller embodimentof a high ratio rolling contact speed change device;

FIG. 5 is a section detail view of the device of FIG. 4;

FIG. 6 shows the device of FIG. 1 arranged to move a mechanical arm;

FIG. 7 is an isometric view of an embodiment of a high ratio rollingcontact speed change device with additional output rings to provideadditional torque;

FIG. 8 is a cutaway view of the embodiment of FIG. 7;

FIG. 9 shows the view of FIG. 8 with the upper housing removed;

FIG. 10 shows the view of FIG. 9 with the lower housing removed;

FIG. 11 shows the view of FIG. 10 with the sun roller removed;

FIG. 12 shows the view of FIG. 11 with the floating sun rings removed;

FIG. 13 is an isometric view of a further embodiment of a high ratiorolling contact speed change device;

FIG. 14 shows the embodiment of FIG. 13 from a different orientation;

FIG. 15 shows a cutaway view of the embodiment of FIG. 13;

FIG. 16 shows the view of FIG. 15 with end outer housings removed;

FIG. 17 shows the view of FIG. 16 with a race associated with the endouter housing also removed;

FIG. 18 shows the view of FIG. 17 with the middle outer housing removed;and

FIG. 19 shows a closeup view of a portion of the view of FIG. 18;

FIG. 20 is a isometric section view of an embodiment with taperedrollers;

FIG. 21 is a closeup of a tapered portion of the embodiment of FIG. 20;

FIG. 22 is a section view of the embodiment of FIG. 20;

FIG. 23 shows a simplified section view of an embodiment with gearedfixed and outer rings, geared rollers to transmit torque between these,and a rolling contact sun ring-to-roller interface;

FIG. 24 shows a closeup view of a variation of the embodiment of FIG. 23combining geared and rolling surfaces;

FIG. 25 shows an exemplary geared embodiment;

FIG. 26 shows an isometric view of the embodiment of FIG. 25;

FIGS. 27B and 28B show section views on the planes 150 and 152 indicatedby FIGS. 27A and 28A respectively;

FIG. 29 shows an isometric cutaway view of a planet carrier; and

FIG. 30 shows an isometric cutaway view of the planet carrier of FIG. 29in a gear system.

DETAILED DESCRIPTION

In an embodiment there is disclosed an apparatus for transmitting powerthrough circular motion while providing the option of a high rotationalspeed ratio as well as torque multiplication that is approximatelyproportional to the rotational speed ratio (save minus various lossessuch as rolling friction). A preferred embodiment uses 100% rollingcontact traction force to transfer torque from the fixed member(s) tothe output member(s) via the planet rollers and sun roller input.Advantages of certain embodiments include, but are not limited to lightweight, small size, low noise creation, smooth operation, highstiffness, and relatively high torque for a friction torque transferdevice. The device can also be constructed with a hollow sun roller (asshown in FIGS. 1 through 6) for cable access in applications such asrobotic and bionic joints. Rolling contact also has the benefit of zerobacklash and high resolution for precision positioning such as formedical and industrial robots. Rolling contact allows the contactmembers to slide in an over-torque scenario acting as a failsafemechanism to reduce or eliminate damage.

Referring now to the device in more detail, in FIG. 1 to FIG. 3 there isshown the preferred embodiment of the present device. Two ring members20 are fastened to a fixed member (not shown), rendering them fixed. Inthe embodiment shown, fixed ring members 20 have fixed ring attachmentflanges 22 for connecting to the fixed member. The mechanism for fixingthe rings is not shown; it may be moveable if the device is part of alarger assembly. Henceforth, the rings will be referred to as “fixed”for the purposes of this disclosure. Conversely, the two “fixed” membersin this example may be used as the output members and the “outputmember” in this example may be fixed. Fixed ring members may be attachedto each other or to another common member. The fixed rings may berotationally fixed together with an integrated housing and/or anexternal structure, such as base 42 shown in FIG. 6, to maintainalignment of the symmetrical forces acting on the rollers.

Output ring 24 is fastened to an output member (not shown) to move theoutput member. In the embodiment shown in FIGS. 1-3, output ring 24 hasoutput ring attachment flanges 26 for connecting to the output member. Asun roller 28 is positioned coaxially within the output and fixed rings.Planet rollers 30 are arranged around the sun roller and within theoutput and fixed rings, in rolling contact with the sun roller and theoutput and fixed rings. Planet rollers 30 have a first portion of afirst diameter in rolling contact with the fixed output ring(s) and asecond portion of a second diameter in rolling contact with the outputring(s). In the embodiment shown, the planet rollers 30 have a largerdiameter at their ends 32 to contact the fixed rings 20, and a smallerdiameter in the middle 34 to contact the output ring 24. In theembodiment shown, the sun roller contacts only the larger diameter ofthe planet rollers.

In further detail, still referring to the invention of FIG. 1 to FIG .3,the purpose of having two fixed rings is to reduce or eliminate twistingforces on the planet rollers. The symmetrical roller shape across thecenter plane with two fixed races, one at each end, results in balancedforces (equal tangential force on the rollers across the center plane)reducing twisting forces (around a radial line from the device axisthrough the center point of a roller axis) and reduces or eliminates theneed for a carrier to ensure the rollers stay aligned. With a fixedcontact patch on either end of each roller, and a single output contactpatch in the middle of each roller, a bearing cage (which may or may notbe used, and which is not shown in these examples) is only beneficial toguide the rollers and to keep the rollers from contacting each other.This bearing cage functions much like a bearing cage in a rollingelement bearing. In other words, a bearing “cage” is not required totransfer load from the fixed ring(s) to the output ring(s) because theforces on the planet rollers are balanced in such a way that there isvery little or no force causing the planet rollers to twist from theirintended rotational axis. The bearing “cage” can be external to therollers as with a conventional bearing cage, or it can be internal tothe rollers more like a planet carrier in a conventional planetary gearreducer. The speed change ratio is accomplished primarily by thedifference in the internal diameter of the fixed rings compared to theinternal diameter of the output rings. The inner and outer contactsurfaces of the planet rollers have the same diameter difference as thedifference between the outer ring(s) contact surface diameters. Thecloser these diameters are to each other, the higher the final speedchange ratio. The fixed ring(s) may be smaller or larger than the outputring(s). Gears would also provide the function of spacing the rollers.

The sun roller has the effect of providing a rolling contact preload forthe planets against the rings. The sun roller also contributes to thespeed change ratio. The smaller the sun roller is, the greater thereduction ratio is between the input and output. The sun roller may bedriven by hand or by a motor or by other means. The sun roller may alsobe the output member if the device is used as a speed increaser.

The sun roller and/or the planet rollers and/or the ring member(s)preferably have elastic and other material properties that allow thesystem to be preloaded, to provide the required traction force. Theexample in FIG. 1 to FIG. 3 is made of steel. It has ring inner contactsurface diameters of 2 inches and is designed to achieve a torque outputtorque of 20 foot pounds.

One embodiment of the present invention provides preload by the use of asplit outer housing. The split housing ring has clamping tabs that canbe actuated by a screw, a spring, or any other method. This split outerring can be used in conjunction with in section compressible outer raceto provide preload by reducing the ID of the thin section outer race andat the same time keep it circular in shape as a result of the shape ofthe split outer housing. The split outer ring provides ease ofmanufacture, means for self-adjustability, and means for adjustablepreload.

The construction details of the invention as shown in FIG. 1 to FIG. 3are the following. Many materials may also be used such as, but notlimited to, steel rings with steel, ceramic, or carbide rollers.Specialized high friction ceramics such as alumina or toughened aluminamay be used in certain applications in order to achieve differentperformance characteristics. Care must be taken to ensure that thethermal expansion properties of the materials are considered so that thepreload provides adequate traction force throughout the entire range ofoperating temperatures. Steel rings with carbide planet rollers combinedwith a sun gear material which has a high enough thermal expansioncoefficient to compensate for the lower expansion ratio of the carbideplanet rollers is a good choice for higher load applications. Using theembodiment shown in FIGS. 4 and 5, with smaller diameter planet rollers(as shown) reduces the effect of the lower thermal expansion ratio ofthe rollers.

Traction fluid may also be used to increase traction and reduce materialcontact. Traction fluid does not provide increased traction at lowspeeds or in reversing applications. A material combination which meetsor exceeds the high speed traction fluid coefficient is necessary whenthe device is moving slowly, stopped or reversing. Steel on carbide isan example of a material combination which the inventors have found tohave these characteristics. Carbide planet rollers have the advantage ofproviding higher torque transfer stiffness.

Other material combinations can include any or all of the componentsmade of or coated with a resilient material such as, but not limited to,polyurethane. One embodiment which is envisioned would use steel oraluminum planet rollers with a textured surface which would interfacewith a resilient layer between the planet rollers and the fixed andoutput rings. This would provide a very quiet device which may be idealfor prosthetics, where stiffness is less of a concern and somecompliance would actually be a benefit.

Gear teeth, either helical or straight cut, or herringbone, may also beused to increase the invention's torque capacity. Gear teeth may be usedby themselves or in combination with the rolling elements shown above(for example geared outer race interface with geared sections of planetgears and a rolling interface between the sun gear input and theplanets. Note that the gears would have pitch diameters equal to therolling elements to which they are attached. Gears would provide highertorque in many applications, but would not provide the same level ofsmoothness and quietness of rolling “traction contact” as describedabove.

In FIGS. 4 and 5, a floating, non-driven, secondary sun roller 36 isused to provide radial preload on the inner diameter of the planetrollers. This is especially helpful in providing consistent contactpressure when smaller diameter planet rollers are used. The floatingsecondary sun roller is free to rotate at a different speed then the sunring input. This design may also be used to maintain planet rollerposition in the axial direction. In the embodiment shown the floatingsun roller is in rolling contact with middle portion 34 of the planetrollers, and sun roller 28 is arranged to contact the planet rollers ateither end. For ease of manufacture the sun roller may be made of twopieces joined together at join 38 as shown in FIG. 5. Floating secondarysun rollers can also be used to provide radial preload on the outerdiameters (at either end) of the planet rollers with the driven sunroller contacting the inner diameters of the planet rollers. This wouldeliminate the need for a two piece sun roller system as shown in FIG. 5.

FIG. 6 shows the embodiment of FIGS. 1-3 arranged to move a mechanicalarm 40. Fixed ring attachment flanges 22 are attached to a base 42 andoutput ring attachment flanges 26 are attached to arm 40.

Variations

Many different variations and embodiments are possible and anticipatedby the inventor. The embodiments and variations disclosed here areintended to describe the basic operating principles of the device and todescribe several of the preferred embodiments for various applications.

Variations can include more than one output member (possibly withdifferent speed change ratios; the use of a planet carrier with rollingelement bearings to eliminate the need for a sun gear input (In thiscase the planet carrier would be driven). An example planet carrierwhich could be used as a drive element is shown in FIGS. 29 and 30. Asingle fixed member and single output member can be used if a planetcarrier is used which prevents the twisting of the planet rollers axes.Tapered rollers can also be used and have the advantage of providing ameans of increasing or adjusting preload (by moving races or rollersaxially) but tapered rollers are believed to increase friction andtherefore reduce efficiency. FIG. 29 shows an isometric cutaway view ofa planet carrier 160. The planet carrier 160, also known as a spider,has planet engaging elements 162, here cylindrical components eachconfigured to fit within a planet roller ; and connecting elements 164connecting the planet engaging elements. FIG. 30 shows an isometriccutaway view of the planet carrier of FIG. 29 in a gear system. Here youcan see how planet engaging element 162 fits within roller 30.

Crowning the contact surfaces (ie: creating a slight curvature so thesurfaces are not completely cylindrical) of the sun roller and/or theplanet rollers and/or the rings is preferable in high load applicationsto more evenly distribute forces across the entire contact patch.Varying the wall thickness along the axial length of the sun and/orplanet and/or ring members is another way to control the forcedistribution.

FIGS. 1-5 all illustrate the basic embodiment of the device with a fewvariations such as different numbers of planets, different ratios ofsun, planets, and outer ring sizes, and the use of a floating sun ringin some images. It uses two fixed outer rings which are bolted directlytogether or to a common rigid component such as but not limited to arobotic arm or robotic base.

FIG. 7 illustrates an embodiment designed for additional torque such asfor, but not limited to, the movement of a telescope or other beamstructure. Four upper housing outer rings 50 are attached to the upperhousing 52 which in this embodiment would be movable (or fixed). 3 lowerhousing outer rings 54 are attached to the lower housing 56 (by anynumber of rings could be used). The advantage of this system includesincreased load on the rollers with less bending deflection due to moreconsistent loading of the rollers.

This embodiment uses the split outer housing shown here on the uppermosthousing. This housing can be bolted together to reduce the insidediameter of the outer race. FIG. 8 shows a section view of theembodiment of FIG. 7. There are 3 floating sun rings 58 in thisembodiment. FIG. 9 shows the view of FIG. 8 with the upper housing 52and upper housing outer rings 50 removed in order to better see thelower housing 56 and lower housing outer rings 54. FIG. 10 shows thesame view, in greater magnification, with the lower housing 56 and lowerhousing outer rings 54 also removed.

FIG. 11 shows the view of FIG. 10 with the sun roller removed to bettersee the floating sun rings 58.The floating sun rings 58 are axiallybetween the contacts of the sun roller with the planets, and are onlycontacting the planets to keep them from bending inward.

FIG. 12 shows the view of FIG. 11 with the floating sun rings 58 alsoremoved. Roller cage 60 can optionally provide stability for rollerswith bearings or other elements. Cage 60 is shown at one end of therollers only in FIGS. 7-12 but would be present at both ends of therollers.

FIG. 13 is an isometric view of a further embodiment of a high ratiorolling contact speed change device, also shown in FIG. 14-19.

In the embodiment of FIGS. 13-19, thin section outer races 70 and 72 arepressed into thicker section outer housing(s) 74 and 76. Preferably, inorder to insert the races the outer housings can be increased in size byopening up the slots in the housings, or possibly by thermally expandingthem. The hardened race can be a heavier, stiffer material.

The embodiment of FIGS. 13-19 uses a preferably harder material such as,but not limited to hardened steel or ceramic for the outer races. Thismaterial is press fit into or clamped into the outer housing members.Also, components are thin section where ever possible to reduce weight.A middle outer housing 74 acts as either output or fixed element, andend outer housings 76 act as the other of output or fixed element. Theend outer housing components 76 are intended to be bolted together, orto the same component so that they act as one piece.

FIG. 15 shows a cutaway view of the embodiment of FIG. 13. The innerrace 78 shown here and in FIGS. 16-19 has a tapered interface with thesun roller drive so that it can be actually moved together, preferablywith the threaded not as shown on one end (but not shown on the other inthis image). This tapered interface allows assembly with reducedinterference or no interference, and expansion of these sun races toincrease the preload of the system. This can also be used to make up forwear over time. As with a number of these embodiments, the rollers canbe larger diameter at either end (respective tapered portions narrowinwardly) instead of toward the center as shown above (respectivetapered portions narrow outwardly).

In an embodiment of the device shown in FIGS. 20-22, the rollers 30 aretapered toward both ends at an angle X. The roller wall are thin enoughto allow elliptical deformation within the elastic limit of thematerial. The fixed rings 20 are also tapered inward toward the axialouter edges but at an angle which is greater than the roller angle bythe ratio of roller outer diameter (OD) to fixed ring inner diameter(ID). For example, if the rollers are 1″ in diameter at an axial plane(EG Plane 1 in FIGS. 1 and 3) and the fixed ring is 10″ in diameter onthat plane, the taper of the rollers may be 0.1 degree and the taper ofthe fixed ring will be 1 degree. As shown in FIG. 21, the rollers haveinterference 84 with the fixed ring taper before assembly. As a result,the rollers can be preloaded so all or part of the roller taper contactsall or part of the ID fix ring taper with the elastic compression of therollers allowing the desired line contact. Matching the taper angleratio with the diameter ratio allows both taper surfaces to maintainrolling contact with little or no sliding because the ratio ofcircumferential length of the roller OD's is equal or near equal to thecircumferential length of the fixed ring ID at all points of contactbetween the two tapers. The advantage of the tapered engagement is axialpositioning of the rollers to reduce or eliminate the need for analignment cage and bearings for the rollers. In the embodiment shownoutput ring 24 has a cylindrical ID but it can be differently shaped. Asshown in FIG. 20, a housing 82 preferably connects both fixed ringstogether. Sun ring 28 provides radial load on rollers and input torqueand can be driven by various means such as but not limited to a directdrive electric motor (not shown).

Another way to define the ratio of the tapered rollers to the taperedfixed ring, is to measure the OD of the roller and the ID of the ringalong two or more planes 80 a, 80 b at different distances from thecenter plane as shown in FIG. 22. The ratio of the roller OD to thefixed ring ID is preferably the same or similar at the intersection 86 awith plane 80 a as at intersection 86 b with plane 80 b. The closerthese ratios are to equal, the less sliding there will be while rolling.

Variations to this embodiment anticipated by the inventor includecrowning of the tapered contact surfaces for various effects.

FIG. 23 shows a simplified section view of an embodiment with gearedfixed and outer rings, geared rollers to transmit torque between these,and a rolling contact sun ring-to-roller interface. the sun ring inputis provided by a roller engagement (sun ring elements 90 and 92). Thesun ring interface is shown as tapered for self-centering but can becylindrical or other shapes.

The roller gears 94 and 96 on roller 30 are not shown with teeth forsimplicity of illustration. Fixed gear 98 is also simplified as isoutput gear 100.

The sun ring parts 90 and 92 are preferably rotationally fixed togetherwith the linear bearings (two larger balls shown near ID of sun), and aspring is optionally used (four small section circles in a taperedarray) to provide the required preload on the tapered sun faces.

An array of electromagnets (not shown but intended to be fixed to thehousing 108 inside the rectangular opening 102 in the sun ring parts)pulls on the permanent magnets (one shown as element 104, but the holes106 in element 90 will house them as well) to provide rotary input andalso to pull the two halves of the sun together for greater traction andgear tooth radial loading when required under higher loads.

FIG. 24 shows a closeup view of a variation of the embodiment of FIG. 23combining geared and rolling surfaces. Although geared is used here incontrast to rolling, in the claims the term “rolling” should beinterpreted to encompass geared as well. Interfaces 110 have rollingcontact and interfaces 112 are geared interfaces. The rolling surfacesare preferably at or near the the pitch diameters of the gears.

FIGS. 25-27B show an exemplary geared embodiment. The gears shown hereare helical, but could be spur gears or other types. Aspects of thisembodiment can apply to other embodiments.

The sun components 120 and 122 are rotationally attached to the fixedhousing 124 with two bearings 126. Sun gear 128 provides rotationalinput to the rollers 130 with one roller shown here but an array ofrollers is preferred. The roller gear 128 interfaces to the output gear132 which is fixed to the output member 134. The fixed members 136 arerigidly attached to the housing members 124 which ensure that they donot rotate relative to each other. The gears 138 on both ends of therollers are fixed to the roller (such as by press fitting or bonding)and mesh with the fixed gears 140 with are fixed to the fixed members136.

Sun components 120 and 122 can be rotationally driven by many differentmeans. Shown here as an example are an array of permanent magnets 142which are acted on by the schematic electro magnets 144. Air orhydraulic input to rotate the sun are other non-limiting examples ofrotary input options. The two large bearings 146 between the fixed andoutput members rotationally support the output gear and output memberrelative to the fixed housing/members.

L-shaped members 148 on the sun components are optional and can slideaxially and preferably spring inward (springs not shown) to provide arolling contact between the blue sun member and the rollers, therebyreducing the gear cogging of the sun gear if it were to be radiallypreloaded. By making the geared rollers thin walled enough, they canelastically deform to make up for size variations due to manufacturingand heat expansion or wear.

FIG. 26 shows an isometric view of the embodiment of FIG. 25, and FIGS.27B and 28B show section views on the planes 150 and 152 indicated byFIGS. 27A and 28A respectively.

While the foregoing written description of the invention enables one ofordinary skill to make and use what is considered presently to be thebest mode thereof, those of ordinary skill will understand andappreciate the existence of variations, combinations, and equivalents ofthe specific embodiment, method, and examples herein. The inventionshould therefore not be limited by the above described embodiment,method, and examples, but by all embodiments and methods within thescope and spirit of the invention.

Immaterial modifications may be made to the embodiments described herewithout departing from what is covered by the claims.

In the claims, the word “comprising” is used in its inclusive sense anddoes not exclude other elements being present. The indefinite articles“a” and “an” before a claim feature do not exclude more than one of thefeature being present. Each one of the individual features describedhere may be used in one or more embodiments and is not, by virtue onlyof being described here, to be construed as essential to all embodimentsas defined by the claims.

The embodiments of the invention in which an exclusive property orprivilege is claimed are defined as follows:
 1. A drive systemcomprising: rollers, each roller having a first portion of a firstdiameter and a second portion of a second diameter, the rollers beingplanet rollers; a fixed outer ring arranged in rolling contact with therespective first portion of each roller; an outer drive or driven ringarranged in rolling contact with the respective second portion of eachroller; a sun drive roller arranged in rolling contact with the planetrollers; and a floating sun roller arranged in rolling contact with therespective second portion of each roller, the sun drive roller beingarranged in rolling contact with the respective first portion of eachroller.
 2. The drive system of claim 1 arranged as a speed reducer inwhich the sun drive roller provides an input and the outer driven ringprovides an output.
 3. The drive system of claim 1 arranged as a speedincreaser in which the sun drive roller provides an output and the outerdrive ring provides an input.
 4. The drive system of claim 1 furthercomprising a planet carrier drive element arranged to rotate with theplanet rollers around an axis defined by the outer drive or driven ring.5. The drive system of claim 4 arranged as a speed reducer in which theplanet carrier drive element provides an input and the outer driven ringprovides an output.
 6. The drive system of claim 4 arranged as a speedincreaser in which the planet carrier drive element provides an outputand the outer drive ring provides an input.
 7. The drive system of claim4 further comprising a first floating sun roller arranged in rollingcontact with the respective first portion of each planet roller and asecond floating sun roller arranged in rolling contact with therespective second portion of each planet roller.
 8. The drive system ofclaim 1 in which the first diameter is greater than the second diameter.9. The drive system of claim 1 in which the first diameter is less thanthe second diameter.
 10. The drive system of claim 1 in which the fixedouter ring is a first fixed outer ring and the drive system furthercomprises a second fixed outer ring, the first fixed outer ring and thesecond fixed outer ring being arranged symmetrically one on each side ofthe outer drive or driven ring.
 11. The drive system of claim 1 in whichthe outer drive or driven ring is a first outer drive or driven ring andthe drive system further comprises a second outer drive or driven ring,the first outer drive or driven ring and the second outer drive ordriven ring being arranged symmetrically one on each side of the fixedouter ring, and being connected to each other to rotate together. 12.The drive system of claim 1 further comprising gear teeth on one or morepairs of surfaces in rolling contact.
 13. The drive system of claim 1 inwhich the planet rollers are tapered, with respective tapered portionsnarrowing inwardly or outwardly.
 14. The drive system of claim 13 inwhich surfaces contacting the respective tapered portions arecorrespondingly tapered.
 15. The drive system of claim 14 in which thesurfaces contacting the respective tapered portions are tapered inratios corresponding to the ratios of the diameters of the respectivetapered portions at the contacting surfaces.
 16. The drive system ofclaim 1 in which the planet rollers have a reflective symmetry withrespect to a plane, the planet rollers defining respective axesperpendicular to the plane.
 17. The drive system of claim 16 in whichelements of the sun drive roller in rolling contact with the planetrollers define axes perpendicular to the plane and collectively have areflective symmetry with respect to the plane.
 18. The drive system ofclaim 1 in which the planet rollers are hollow.
 19. A drive systemcomprising: rollers, each roller having a first portion of a firstdiameter and a second portion of a second diameter, the rollers beingplanet rollers; a fixed outer ring arranged in rolling contact with therespective first portion of each roller; an outer drive or driven ringarranged in rolling contact with the respective second portion of eachroller; a sun drive roller arranged in rolling contact with the planetrollers; and a floating sun roller arranged in rolling contact with therespective first portion of each roller, the sun drive roller beingarranged in rolling contact with the respective second portion of eachroller.
 20. The drive system of claim 19 arranged as a speed reducer inwhich the sun drive roller provides an input and the outer driven ringprovides an output.
 21. The drive system of claim 19 arranged as a speedincreaser in which the sun drive roller provides an output and the outerdrive ring provides an input.
 22. The drive system of claim 19 furthercomprising a planet carrier drive element arranged to rotate with theplanet rollers around an axis defined by the outer drive or driven ring.23. The drive system of claim 22 arranged as a speed reducer in whichthe planet carrier drive element provides an input and the outer drivenring provides an output.
 24. The drive system of claim 22 arranged as aspeed increaser in which the planet carrier drive element provides anoutput and the outer drive ring provides an input.
 25. The drive systemof claim 19 in which the first diameter is greater than the seconddiameter.
 26. The drive system of claim 19 in which the first diameteris less than the second diameter.
 27. The drive system of claim 19further comprising gear teeth on one or more pairs of surfaces inrolling contact.
 28. The drive system of claim 19 in which the planetrollers are tapered, with respective tapered portions narrowing inwardlyor outwardly.
 29. The drive system of claim 28 in which surfacescontacting the respective tapered portions are correspondingly tapered.30. The drive system of claim 29 in which the surfaces contacting therespective tapered portions are tapered in ratios corresponding to theratios of the diameters of the respective tapered portions at thecontacting surfaces.
 31. The drive system of claim 19 in which theplanet rollers have a reflective symmetry with respect to a plane, theplanet rollers defining respective axes perpendicular to the plane. 32.The drive system of claim 31 in which elements of the sun drive rollerin rolling contact with the planet rollers define axes perpendicular tothe plane and collectively have a reflective symmetry with respect tothe plane.
 33. The drive system of claim 19 in which the planet rollersare hollow.
 34. A drive system comprising: rollers, each roller having afirst portion of a first diameter and a second portion of a seconddiameter, the rollers being planet rollers; a fixed outer ring arrangedin rolling contact with the respective first portion of each roller; anouter drive or driven ring arranged in rolling contact with therespective second portion of each roller; a sun drive roller arranged inrolling contact with the planet rollers; a planet carrier drive elementarranged to rotate with the planet rollers around an axis defined by theouter drive or driven ring; and a first floating sun roller arranged inrolling contact with the respective first portion of each planet rollerand a second floating sun roller arranged in rolling contact with therespective second portion of each planet roller.
 35. The drive system ofclaim 34 further comprising gear teeth on one or more pairs of surfacesin rolling contact.
 36. The drive system of claim 34 in which the planetrollers are tapered, with respective tapered portions narrowing inwardlyor outwardly.
 37. The drive system of claim 36 in which surfacescontacting the respective tapered portions are correspondingly tapered.38. The drive system of claim 37 in which the surfaces contacting therespective tapered portions are tapered in ratios corresponding to theratios of the diameters of the respective tapered portions at thecontacting surfaces.
 39. The drive system of claim 34 in which theplanet rollers have a reflective symmetry with respect to a plane, theplanet rollers defining respective axes perpendicular to the plane. 40.The drive system of claim 39 in which elements of the sun drive rollerin rolling contact with the planet rollers define axes perpendicular tothe plane and collectively have a reflective symmetry with respect tothe plane.
 41. The drive system of claim 34 in which the planet rollersare hollow.
 42. A drive system comprising: rollers, each roller having afirst portion of a first diameter and a second portion of a seconddiameter; a fixed outer ring arranged in rolling contact with therespective first portion of each roller; and an outer drive or drivenring arranged in rolling contact with the respective second portion ofeach roller; in which the fixed outer ring is a first fixed outer ringand the drive system further comprises a second fixed outer ring, thefirst fixed outer ring and the second fixed outer ring being arrangedsymmetrically one on each side of the outer drive or driven ring. 43.The drive system of claim 42 further comprising gear teeth on one ormore pairs of surfaces in rolling contact.
 44. The drive system of claim42 in which the rollers are tapered, with respective tapered portionsnarrowing inwardly or outwardly.
 45. The drive system of claim 44 inwhich surfaces contacting the respective tapered portions arecorrespondingly tapered.
 46. The drive system of claim 45 in which thesurfaces contacting the respective tapered portions are tapered inratios corresponding to the ratios of the diameters of the respectivetapered portions at the contacting surfaces.
 47. The drive system ofclaim 42 in which the rollers have a reflective symmetry with respect toa plane, the rollers defining respective axes perpendicular to theplane.
 48. The drive system of claim 47 in which the rollers are planetrollers, the drive system further comprising a sun drive roller arrangedin rolling contact with the planet rollers, and in which elements of thesun drive roller in rolling contact with the planet rollers define axesperpendicular to the plane and collectively have a reflective symmetrywith respect to the plane.
 49. The drive system of claim 42 in which thefirst fixed outer ring and the second fixed outer ring are connected toeach other.
 50. The drive system of claim 49 in which the rollers areplanet rollers, the drive system further comprising a sun drive rollerarranged in rolling contact with the planet rollers, and in which thefirst fixed outer ring and the second fixed outer ring are connected toeach other via a connection portion axially traversing an axial throughhole of the sun drive roller.
 51. The drive system of claim 42 in whichthe rollers are hollow.
 52. A drive system comprising: rollers, eachroller having a first portion of a first diameter and a second portionof a second diameter; a fixed outer ring arranged in rolling contactwith the respective first portion of each roller; and an outer drive ordriven ring arranged in rolling contact with the respective secondportion of each roller; in which the outer drive or driven ring is afirst outer drive or driven ring and the drive system further comprisesa second outer drive or driven ring, the first outer drive or drivenring and the second outer drive or driven ring being arrangedsymmetrically one on each side of the fixed outer ring, and beingconnected to each other to rotate together.
 53. The drive system ofclaim 52 further comprising gear teeth on one or more pairs of surfacesin rolling contact.
 54. The drive system of claim 52 in which therollers are tapered, with respective tapered portions narrowing inwardlyor outwardly.
 55. The drive system of claim 54 in which surfacescontacting the respective tapered portions are correspondingly tapered.56. The drive system of claim 55 in which the surfaces contacting therespective tapered portions are tapered in ratios corresponding to theratios of the diameters of the respective tapered portions at thecontacting surfaces.
 57. The drive system of claim 52 in which therollers have a reflective symmetry with respect to a plane, the rollersdefining respective axes perpendicular to the plane.
 58. The drivesystem of claim 57 in which the rollers are planet rollers, the drivesystem further comprising a sun drive roller arranged in rolling contactwith the planet rollers, and in which elements of the sun drive rollerin rolling contact with the planet rollers define axes perpendicular tothe plane and collectively have a reflective symmetry with respect tothe plane.
 59. The drive system of claim 52 in which the rollers arehollow.
 60. A drive system comprising: rollers, each roller having afirst portion of a first diameter and a second portion of a seconddiameter, the rollers being planet rollers; a fixed outer ring arrangedin rolling contact with the respective first portion of each roller; anouter drive or driven ring arranged in rolling contact with therespective second portion of each roller; and a sun drive rollerarranged in rolling contact with the planet rollers; in which the planetrollers have a reflective symmetry with respect to a plane, the rollersdefining respective axes perpendicular to the plane.
 61. The drivesystem of claim 60 further comprising gear teeth on one or more pairs ofsurfaces in rolling contact.
 62. The drive system of claim 60 in whichthe planet rollers are tapered, with respective tapered portionsnarrowing inwardly or outwardly.
 63. The drive system of claim 62 inwhich surfaces contacting the respective tapered portions arecorrespondingly tapered.
 64. The drive system of claim 63 in which thesurfaces contacting the respective tapered portions are tapered inratios corresponding to the ratios of the diameters of the respectivetapered portions at the contacting surfaces.
 65. The drive system ofclaim 60 in which the planet rollers have a reflective symmetry withrespect to a plane, the planet rollers defining respective axesperpendicular to the plane.
 66. The drive system of claim 65 in whichelements of the sun drive roller in rolling contact with the planetrollers define axes perpendicular to the plane and collectively have areflective symmetry with respect to the plane.
 67. The drive system ofclaim 60 in which the fixed outer ring is a first fixed outer ring andthe drive system further comprises a second fixed outer ring, the firstfixed outer ring and the second fixed outer ring being arrangedsymmetrically one on each side of the outer drive or driven ring. 68.The drive system of claim 67 in which the first fixed outer ring and thesecond fixed outer ring are connected to each other.
 69. The drivesystem of claim 68 in which the first fixed outer ring and the secondfixed outer ring are connected to each other via a connection portionaxially traversing an axial through hole of the sun drive roller. 70.The drive system of claim 60 in which the planet rollers are hollow.